1. Field of the Invention
The present invention relates to a solid oxide fuel cell and a method of manufacturing the same.
2. Description of the Related Art
A solid oxide fuel cell undergoes an electrode reaction at a three-phase interface of a solid electrolyte, an electrode and a gas phase. In order to improve electric power generation performance of a fuel cell, therefore, it is necessary that the area of the interface between the solid electrolyte and the electrode, i.e., a joint surface, (which is sometimes referred to as an effective interface area) is enlarged as much as possible so as to reduce the interface resistance, whereby the electrode reaction is accelerated. The enlargement of the effective interface area between the solid electrolyte and the electrode also improves the mechanical joint strength between the solid electrolyte and the electrode.
In order to enlarge the effective interface area between the solid electrolyte and the electrode, such a method has been practiced that a surface of an electrolyte is roughened so as to form roughness on the surface (as described, for example, in JP-A-7-073890) The method for forming the roughened surface includes a coarse particle applying method, a sandpaper pressing method and a sand blasting method.
For example, such a method has been proposed that particles are applied and attached to a surface of a mother body and sintered simultaneously with the mother body so as to form a large number of convex portions on the surface of the mother body, and then an electrode is attached to the surface having the convex portions formed thereon (as described, for example, in JP-A-62-045596 and JP-A-56-160653).
Such a method has been also proposed that a roughened surface is formed by making coarse particles present only on a part of an electrode, which is in contact with a solid electrolyte, but not present on the other parts thereof, by a slurry method or a thermal spraying method (as described, for example, in Japanese Patent No. 2,695,641).
In all of the related methods for forming a roughened surface, a roughened surface cannot be obtained effectively with respect to the complicated operation or high cost of the methods. FIG. 8 is a schematic cross sectional view showing a roughened surface of a solid electrolyte formed by the related methods for forming a roughened surface. Although a roughened surface can be formed on a solid electrolyte 51, for example, by a sand blasting method, repetition frequency of roughness on the roughened surface (which is sometimes referred to as a roughness frequency) is almost constant as shown in the figure. There is a limitation in enlargement of the effective interface area by the related methods for forming a roughened surface, and therefore, improvement in electric power generation performance of a fuel cell is also limited.